In drip irrigation two factors are of utmost importance. First, the flow rate onto the crop must be controlled. A conventional technique for flow rate adjustment is to change the number of emitters as the need for changes in flow rate occurs. For example, in an orchard the number of emitters can be increased as the trees grow in order to provide increased flow rates. This procedure requires an excessive number of emitter valves, increases labor costs to install the additional valves, and provides only stepwise adjustment in flow rate.
A second important factor is compensating for inlet water pressure fluctuations. Such pressure fluctuations may be caused by varying source pressures and/or varying elevations in the field being irrigated.
Copending application Ser. No. 596,222 filed on July 16, 1975 discloses a drip irrigation valve which has both flow control and pressure compensating features. Combining these features in a single drip irrigation valve is most desirable. However, with my prior valve, pressure compensation is achieved by using the inlet pressure to the valve to deform a resilient seal into a groove. Although this is satisfactory, it requires relatively careful control of the hardness of the resilient material of the seal.